JPH0638647B2 - Input circuit of synchronization judgment device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input circuit of a synchronization determination device provided in a television receiver.

2. Description of the Related Art In a television receiver, when performing automatic search tuning, a tuning circuit sequentially changes a tuning voltage applied to a tuner in an up direction or a down direction, but the tuning voltage is stopped at a tuning position ( Therefore, a stop control signal is required to stop the automatic search. As such a step control signal, a synchronizing signal of a received television signal is generally used. That is, the synchronization signal cannot be obtained when the automatic search operation is between the two broadcasting channels, but the synchronization signal can be obtained when the broadcasting channel is reached. In this case, the synchronization determination device is provided in the channel selection circuit, but generally, the synchronization determination circuit outputs the synchronization signal output from the synchronization separation circuit to the input circuit.

Problems to be Solved by the Invention By the way, the output of the sync separation circuit normally outputs the sync signal (B) from the received video signal (A) of FIG. 3 under normal electric field strength, but when the electric field is weak, noise (N In some cases, as shown in FIG. 4, due to the influence of), etc., the synchronization signals are output as if there were many synchronization signals. In this case, an erroneous determination occurs especially when the synchronization determination device is of a type in which the synchronization signal pulses are counted per fixed time.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an input circuit of a synchronization determination device capable of correctly supplying a synchronization signal even in a weak electric field.

Means for Solving the Problems In order to achieve the above object, in the present invention, in the input circuit of the synchronization determination device for determining the synchronization signal of the received television signal, the period of the synchronization signal as the output of the synchronization separation circuit is flybacked. A configuration is provided in which means for narrowing the limit by the integrated output signal of the pulse is provided.

Effect With such a configuration, the influence of noise can be reduced as much as possible, so that it is possible to suppress generation of a pseudo sync signal due to noise itself.

Example In FIG. 1, a wave is applied to a sand castle shown in FIG. 2 (a) at a point (a). This sandcastle wave is output from the video / chroma processing IC. When using the output of the IC, the circuit (1) shown by the dotted line is added (b).
At that point, the synchronizing signal shown in FIG. 2 (b) is obtained. When using the output of a normal sync separation circuit, the straight line
Since circuit (b) is given, the circuit (1) is unnecessary. By the way, the circuit (1) inputs the sandcastle wave to the base of the emitter follower transistor (Q ₁ ) via the resistor (R ₁ ), and outputs its output at a constant level by the Zener diode (ZD) and the resistor (R ₃ ). The synchronization signal (b) is output by slicing with.

In Fig. 1, the flyback pulse (FP) is at point (c).
Is applied. This flyback pulse (FP) is a resistor (R ₅ )
Waveform shaping as shown in Fig. 2 (d) by (R ₆ ) (R ₇ ) and transistor (Q ₂ ), and further integrated by resistor (R ₈ ) and capacitor (C ₁ ) as shown in (e). ₉ ) Via transistor
Controls on / off of (Q ₃ ). Therefore the integrated waveform (e) only cut-off level (E ₁₎ period is the following transistor (Q _3), the collector side of the synchronizing signal of the transistor (Q ₃₎
(b) is enabled, and for the rest of the time it is disabled by being clamped to approximately ground level. In other words, the period of the synchronization signal (b) is narrowly limited by the integrated output signal (e) of the flyback pulse. Therefore, most of the noise is cut off. Further, the noise within the limited effective period (T) can be removed by the integral action of the resistor (R ₄ ) and the capacitor (C ₂ ).

In this way, in this configuration, even in a weak electric field with a lot of noise, the synchronization signal can be given to the synchronization determination device in an accurate form without being influenced by the noise as shown in FIG. 2 (f).

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to extremely reduce the unnecessary components of the sync separation output due to the influence of noise or the like during a weak electric field. It is possible to correctly make the determination by the synchronization determination device, and the effect is great.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an input circuit of a synchronization determination device embodying the present invention, and FIG. 2 is a signal waveform diagram of each part thereof. 3 and 4 are explanatory views of a conventional example. (b) …… Synchronization signal, (FP) …… Flyback pulse, (C ₁ ) …… Integrating capacitor, (R ₁ ) …… Integrating resistor.

Claims (1)

[Claims] 1. An input circuit of a sync signal judging device for judging a sync signal of a received television signal, wherein a shaping means for shaping a flyback pulse into a rectangular wave narrower than the flyback pulse, and the waveform shaping. An integrating means for integrating the rectangular wave, and a gate means for passing a synchronizing signal in the received television signal in a period in which the signal integrated by the integrating means projects beyond a predetermined level, An input circuit of a synchronization determination device, characterized in that the period of the synchronization signal is narrowed.